refactor(api): remove the deprecated /api/stats endpoint

The only consumer (the marketing landing) now uses /api/v1/stats, so drop
the legacy /api/stats route and its handler. Delete src/routes/stats.ts and
its test; repoint the index CORS test at /api/v1/stats.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/index.test.ts

@@ -45,9 +45,9 @@ describe("CORS middleware", () => {
     );
   });
 
-  it("makes /api/stats readable from any origin", async () => {
+  it("makes /api/v1/stats readable from any origin", async () => {
     const res = await worker.fetch(
-      req("/api/stats", { headers: { Origin: "https://example.com" } }),
+      req("/api/v1/stats", { headers: { Origin: "https://example.com" } }),
       env as unknown as Env,
     );
     expect(res.status).toBe(200);